You don't need a voltage
converter to charge cameras, cell phones or laptops, or really any electronic item. All you need are plug adapters. You can get some decent all in one adapters on
Amazon for under $5.00, which are exactly the same ones I have seen in catalogs and at electronics stores for $25 or more. The only thing you would likely need a voltage converter for is a dual voltage hair dryer and your US dryer won't work very well even with one of these. Most hotels provide them, or you can do as I did, buy a European hair dryer for travel. Many hotels in Europe also provide special outlets in the bathroom for electric shavers so your US one will work there.
As for mini bars, they aren't as common in Europe as in the US, and when you do have one, they are usually filled with stuff the hotel wants you to buy.